(i) Technical Field
The present application relates to a method to control an optical receiver implemented with a semiconductor optical amplifier (hereafter denoted as “SOA” in upstream of a semiconductor photodiode (hereafter denoted as “PD”).
(ii) Related Background Arts
In the optical communication system, an optical signal transmitted from an optical transmitting device is received by an optical receiving device propagating through an optical fiber. For instance, a Japanese Patent Application published as JP-2003-0348021A has disclosed an optical communication system in which the optical signal transmitted from an optical transmitter, propagating in an optical fiber, and finally received by an optical receiver.
The optical receiver often detects the optical signal by a photodiode (hereafter denoted as “PD”) after amplifying the optical signal by a semiconductor optical amplifier (hereafter denoted as “SOA”) because the optical signal is attenuated during the propagating within the optical fiber. In such an arrangement, the light incoming to the SOA is monitored in the magnitude thereof, and the SOA is controlled in feedback based on the monitoring result.
However, when a portion of incoming light provided from the optical fiber is monitored and the SOA is controlled in feedback by the monitoring results, the rest portion of the incoming light provided from the optical fiber and entering the “SOA” is inevitably diminished, which lowers the magnitude of the outgoing light, degrades the noise figure (NF) or the preciseness of the signal detection by the PD, and so on.